1. Technical Field
This invention relates in general to automated media storage libraries and in particular to an automated media storage library with a variable focal length lens for scanning bar coded labels associated with data storage media in the library.
2. Background Art
Automated media storage libraries which utilize storage devices such as data cartridges are well known in the art. A large number of the cartridges are typically mounted in a rotatable housing or magazine and individually indexed with bar coded labels. The labels may be positioned in a variety of locations, including on the cartridges themselves, adjacent to a mail slot on the housing, or on a door around each mail slot. A bar code reader system is located adjacent to the housing for reading the labels so that the desired cartridge may be selected and accessed. In order to scan a label associated with a moving cartridge and/or reader system, the focal length of the reader must be adjustable to accommodate for cartridges and labels which differ in size and, thus, distance from the reader. This problem has become even more acute with libraries which contain multimedia storage devices.
Therefore, it is a feature of the present invention to provide an assembly with a high speed, variable focal length lens for reading bar code labels on media devices located in an automated media storage library.
A bar code reader for an automated storage library has a lens assembly with a pair of polarized liquid crystal lenses. Each lens has pair of parallel glass plates that are separated by upper and lower glass substrates. A series of rectangular polymer films are symmetrically spaced apart between the two glass substrates. Both the substrates and the films are perpendicular to the glass plates. A semi-circular electrode is formed on each side of each piece of film to form a semi-cylindrical xe2x80x9cstackxe2x80x9d of film. The electrodes do not completely cover the film. Liquid crystal fills the space between each adjacent pair of the films. The films are coated and/or treated by an alignment process to predispose the liquid crystals to an alignment and rotation direction.
When a selected voltage is applied between adjacent ones of the electrodes, the liquid crystals are synchronously rotated to alter their refractive index to a desired value. Thus, when the layers of each lens are manipulated in unison, the bar code reader is able to quickly adjust its focal length to read bar codes labels on media devices at various distances. For example, when the applied voltage is zero, there is no refractive index difference between the electrode portion and the non-electrode portion of the liquid crystal. Therefore, the focal length is infinite. Applying a voltage to the electrodes alters the refractive index of the liquid crystal and, thus, shortens the focal length of the lens assembly to the proper distance for reading the labels.